1. Field of the Invention
This invention generally relates to multiple sprocket assemblies for bicycles. More specifically, the present invention relates to a bicycle rear sprocket assembly that is configured to minimize bending of and maintain proper spacing between the sprockets.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle to meet the demands of the riders.
In recent years, as the number of speeds available in bicycle transmissions has increased, the number of sprockets installed on the rear-wheel sprocket assembly of such bicycles has increased seven sprocket wheels or more. As a result, the weight of the bicycle has increased. Thus, there is a desire to reduce the weight of the bicycle. In other words, in pursuit of faster running speed, it is desirable to reduce the weight of all kinds of parts of the bicycle.
In order to reduce the weight of a multiple sprocket assembly, a spider (sprocket support), which supports a plurality of ring-shaped sprocket wheels, has been used. By using a spider, a light metal such as aluminum, etc., is generally used for the spider, while various types of steel materials are used for the sprockets to provide adequate strength. One example of a multiple sprocket assembly that uses a spider is disclosed in U.S. Pat. No. 6,102,821 (assigned to Shimano Inc.). In this patent, two spiders are used with each spider supporting two sprockets. Each spider has a boss part and a plurality of support arms which extend radially outward from the outer circumferential surface of the boss part in directions perpendicular to the axis of the boss part. The sprockets are attached to mounting surfaces on opposite side surfaces of each of the support arms. Accordingly, this construction is greatly improved in terms of weight reduction.
However, one drawback of a multiple sprocket assembly constructed in this manner is that if the spider is made too thin, then the sprocket may deflect towards the adjacent sprocket. This situation can result in degrading the shifting performance of the rear derailleur. On the other hand, if the spider is made thicker, weight of the multiple sprocket assembly increases.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle rear sprocket assembly. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.